Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009

Five years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn's atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0cm-1 spectral resolution are used to retrieve the variation in the...

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Main Authors: Fletcher, L, Achterberg, R, Greathouse, T, Orton, G, Conrath, B, Simon-Miller, A, Teanby, N, Guerlet, S, Irwin, P, Flasar, F
Format: Journal article
Language:English
Published: 2010
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author Fletcher, L
Achterberg, R
Greathouse, T
Orton, G
Conrath, B
Simon-Miller, A
Teanby, N
Guerlet, S
Irwin, P
Flasar, F
author_facet Fletcher, L
Achterberg, R
Greathouse, T
Orton, G
Conrath, B
Simon-Miller, A
Teanby, N
Guerlet, S
Irwin, P
Flasar, F
author_sort Fletcher, L
collection OXFORD
description Five years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn's atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0cm-1 spectral resolution are used to retrieve the variation in the zonal mean temperatures in the stratosphere (0.5-5.0mbar) and upper troposphere (75-800mbar) between October 2004 (shortly after the summer solstice in the southern hemisphere) and July 2009 (shortly before the autumnal equinox).Saturn's northern mid-latitudes show signs of dramatic warming in the stratosphere (by 6-10. K) as they emerge from ring-shadow into springtime conditions, whereas southern mid-latitudes show evidence for cooling (4-6. K). The 40-K asymmetry in stratospheric temperatures between northern and southern hemispheres (at 1. mbar) slowly decreased during the timespan of the observations. Tropospheric temperatures also show temporal variations but with a smaller range, consistent with the increasing radiative time constant of the atmospheric response with increasing pressure. The tropospheric response to the insolation changes shows the largest magnitude at the locations of the broad retrograde jets. Saturn's warm south-polar stratospheric hood has cooled over the course of the mission, but remains present.Stratospheric temperatures are compared to a radiative climate model which accounts for the spatial distribution of the stratospheric coolants. The model successfully predicts the magnitude and morphology of the observed changes at most latitudes. However, the model fails at locations where strong dynamical perturbations dominate the temporal changes in the thermal field, such as the hot polar vortices and the equatorial semi-annual oscillation (Orton, G., and 27 colleagues [2008]. Nature 453, 196-198). Furthermore, observed temperatures in Saturn's ring-shadowed regions are larger than predicted by all radiative-climate models to date due to the incomplete characterization of the dynamical response to the shadow. Finally, far-infrared CIRS spectra are used to demonstrate variability of the para-hydrogen distribution over the 5-year span of the dataset, which may be related to observed changes in Saturn's tropospheric haze in the spring hemisphere. © 2010 Elsevier Inc.
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spelling oxford-uuid:1ad7d224-442d-4f7c-a31b-1ca26923f55b2022-03-26T10:57:05ZSeasonal change on Saturn from Cassini/CIRS observations, 2004-2009Journal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:1ad7d224-442d-4f7c-a31b-1ca26923f55bEnglishSymplectic Elements at Oxford2010Fletcher, LAchterberg, RGreathouse, TOrton, GConrath, BSimon-Miller, ATeanby, NGuerlet, SIrwin, PFlasar, FFive years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn's atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0cm-1 spectral resolution are used to retrieve the variation in the zonal mean temperatures in the stratosphere (0.5-5.0mbar) and upper troposphere (75-800mbar) between October 2004 (shortly after the summer solstice in the southern hemisphere) and July 2009 (shortly before the autumnal equinox).Saturn's northern mid-latitudes show signs of dramatic warming in the stratosphere (by 6-10. K) as they emerge from ring-shadow into springtime conditions, whereas southern mid-latitudes show evidence for cooling (4-6. K). The 40-K asymmetry in stratospheric temperatures between northern and southern hemispheres (at 1. mbar) slowly decreased during the timespan of the observations. Tropospheric temperatures also show temporal variations but with a smaller range, consistent with the increasing radiative time constant of the atmospheric response with increasing pressure. The tropospheric response to the insolation changes shows the largest magnitude at the locations of the broad retrograde jets. Saturn's warm south-polar stratospheric hood has cooled over the course of the mission, but remains present.Stratospheric temperatures are compared to a radiative climate model which accounts for the spatial distribution of the stratospheric coolants. The model successfully predicts the magnitude and morphology of the observed changes at most latitudes. However, the model fails at locations where strong dynamical perturbations dominate the temporal changes in the thermal field, such as the hot polar vortices and the equatorial semi-annual oscillation (Orton, G., and 27 colleagues [2008]. Nature 453, 196-198). Furthermore, observed temperatures in Saturn's ring-shadowed regions are larger than predicted by all radiative-climate models to date due to the incomplete characterization of the dynamical response to the shadow. Finally, far-infrared CIRS spectra are used to demonstrate variability of the para-hydrogen distribution over the 5-year span of the dataset, which may be related to observed changes in Saturn's tropospheric haze in the spring hemisphere. © 2010 Elsevier Inc.
spellingShingle Fletcher, L
Achterberg, R
Greathouse, T
Orton, G
Conrath, B
Simon-Miller, A
Teanby, N
Guerlet, S
Irwin, P
Flasar, F
Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title_full Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title_fullStr Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title_full_unstemmed Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title_short Seasonal change on Saturn from Cassini/CIRS observations, 2004-2009
title_sort seasonal change on saturn from cassini cirs observations 2004 2009
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